The aim of the paper was to estimate how the value of 1 GJ of energy in coal with a calorific value of 5500 kcal/kg varies on the international coal market compared to 1 GJ of energy in coal with a calorific value of 6000 kcal/kg. The analysis of data from different ports was intended to answer the question of whether the pricing of coals of different producers according to their calorific value is convergent. The best-known price standard for thermal coal is 25.1 MJ/kg coal (6000 kcal/kg) and, until recently, coals with such quality parameters dominated international trade. Currently, coals with parameters other than considered to be standard parameters are traded on the coal market, hence it is necessary to price a unit of energy (e.g. 1 GJ) contained in these coals. The indices have been selected of the largest exporters of thermal coal for which data was available and referred to the same coal types (grades) determined on the same basis (FOB). Theoretically, the price differential between 6000 kcal/kg and 5000 kcal/kg coal (in USD/ton) should be (at least) as much as the difference in calorific value, i.e. about 9% per USD/ton. In reality, the price differential between these types of coal is greater, though. The overall conclusion of the analysis is that the price calculated per 1 GJ of energy fluctuated on average by 5.9% over the entire period considered. The analytical results obtained for coal from four countries are quite convergent, so it can be assumed that the calculated relationship between the prices of coal with different calorific values (6000 and 5000 kcal/kg) is a good approximation of the observed relationships in the international trade. The calculation results provide a simple formula allowing to estimate the price of coal with a calorific value other than the standard 25.1 MJ/kg (6000 kcal/kg) using the relationships from the international market.

The paper presents selected issues related to the development of international coal markets. World consumption of coal dropped for the second year in a row in 2016, primarily due to the lower demand from China and the US. The share of coal in global primary energy consumption decreased to 28%. World coal production accounted to 3.66 billion toe and it was lower by 6.2% when compared to the previous year. More than 60% of this decline took place in China. The decline in global production was more than four times higher than the decrease in consumption. The sufficiency of the world resources of coal are estimated at 153 years – that is three times more than the sufficiency of oil and gas resources. After several years of decline, coal prices increased by 77% in 2016. The current spot prices are at the level of $80/ton and are close to the 2014 prices. In the European market, after the first half of the year, coal prices reached the level of around 66% higher than in the same period of the last year. The average price in the first half amounted to PLN 12.6/GJ, which is close to the 2012 prices. The share of spot trade in the total purchase amount accounted to approx. 20%. Prices in futures contracts can be estimated on the basis of the Japan-Australia contracts prices and prices in supplies to power plants located in Germany. On average, the prices in supplies to these power plants were higher by approximately 9% in the years 2010 – 2016 and prices in Australia – Japan contracts were 12% higher than CIF ARA prices in 2017. Global energy coal trade reached about 1.012 billion tons in 2016. A decline by 4.8% is expected in 2019 primarily due to the expected reduction in demand in major importing countries in Asia.